1. Field of the Invention
The present invention relates to improving total fuel consumption and engine output torque of a compound system composed of an engine and a rotary machine. More particularly, the invention relates to a dynamo-electric machine or a turbo dynamo-electric machine attached to an engine that is operated in concert with another dynamo-electric machine. Finally, the invention relates to a vehicle engine usable within a broad spectrum of engine speeds and to a system of rotary machines attached thereto.
2. Description of the Related Art
Generally, many techniques have been proposed in order to improve fuel consumption and torque of engines. An example of an electrical method is generating large amounts of driving energy at high engine speeds with a rotary machine attached to the engine in order to accumulate a form of the energy. The stored energy is used to contribute or increase total generated torque in a low speed region where the engine torque may be insufficient. This is accomplished by making the rotary machine operate electrically with the accumulated energy in concert with the engine.
An example of a mechanical method that is used extensively involves a technique that improves both fuel consumption and torque through supercharging while maintaining an air-to-fuel ratio that achieves excellent fuel consumption. However, the former electrical method, that is, the method of using a large capacity rotary machine, capacitor, or power converter, is troublesome because the system increases in cost, weight, and complexity. Also, the latter mechanical method, that is, turbo supercharging, is complicated in that supercharging is insufficient at low engine speeds because the turbo system does not operate fast enough, whereas at high engine speeds, the turbo system operates too fast to the extent that there is a need to lower the exhaust pressure through bypassing.
The proposed techniques have problems related to cost, weight, and complexity of control with regard to the electro-motive assistance of the engine power. Additionally, there is the problem that the turbo system is insufficient or excessive depending upon an increase of engine combustion energy itself. Besides, only a small advantage has been achieved in improving fuel consumption and torque. Hence, to date, these techniques have not been in widespread use to the extent that they dominate the market.